Cerebral metabolism in vivo was examined in a variety of neurological states including a) ischemia, b) hypothermia and c) paralysis. a) Previous investigations have centered on the biochemical changes which occur both during and after an ischemic insult. With increasing periods of ischemia, there are major perturbations in the recovery of total adenylates, the cyclic nucleotides, glycogen and P-creatine which may adversely affect the restoration of function. Regional studies clearly indicate that many of these pathophysiological events are not limited to the cerebral cortex, but occur elsewhere with varying intensity. Brain slice studies indicate that only adenosine, norepinephrine and histamine are sufficiently active to mediate the postischemic rise in cyclic AMP. b) The relative activities of glycogen phosphorylase and synthase were measured as a function of body temperature in brains from hibernating hamsters. The % phosphorylase a increased with increasing body temperature and was directly proportional to the cyclic AMP levels in the brain. c) Experimentally-induced paralysis affecting the spinal cord neurons had little or no effect on cortical metabolites, but significantly decreased cyclic GMP and increased both GABA and glycogen in the cerebellum.